The present invention concerns the interconnection of subsystems of an electronics system with each other, and more specifically relates to an electrooptical interface for interconnecting such subsystems together via a single-axis, bidirectional free-space optical bus.
Electronics systems of several major types are commonly packaged as a group of fixed or variable subsystems interconnected with each other by a bus carrying signals from one subsystem to the others.
Digital computers are usually designed in this way. A number of individual cards or logic books form subsystems which plug into a backplane bus carrying signals for data, storage addresses, interrupts, and other purposes. One card, for example, may include a processor for executing application programs, while others may include read/write storage, controllers for workstations or displays, adapters for mass storage, or interfaces to local-area networks or communications lines. The functional electronics circuits on each card gain access to the common bus for transmitting data, addresses, and control signals according to a predetermined bus protocol.
This type of packaging has significant advantages. Different numbers of different kinds of subsystems can be configured into the system. Customization of the system is simple enough that often the user can perform it unaided. New functions and improved technology can be incorporated at a later date, without replacing the entire system. Diagnostics and repair of the system are enhanced by the ability to isolate subsystems easily.
Nevertheless, conventional wired backplane buses have their costs and disadvantages. As electronics technology becomes more and more integrated, the connectors for transmitting signals from one unit to another become increasingly expensive and unreliable. This is particularly true of backplane busses, which must withstand repeated insertion cycles, and which must often provide mechanical support and alignment for the subsystems, as well as providing electrical connections.
The art has sought alternatives to the parallel wired ("copper") backplane bus for interconnecting subsystems of an electronics system. The art has even sought out other technologies for implementing such busses. Optical technology in particular has provided a number of ways to replace copper backplane busses. Despite the need to convert high-speed electrical signal to optical signals and back again--and frequently to convert between serial and parallel signals--many people have proposed optical backplane busses of one form or another for a long time.
Yet, for all the various optical backplane busses put forth, conventional copper busses are still the undisputed rulers of the world of presently available electronics systems. Optical signals are transmitted only from one designated point to another designated point, within optical fibers. The major problem seems to be that previous optical busses which could possibly be employed for or adapted to interconnecting large and variable numbers of subsystems are more expensive and unreliable than the wired busses and connectors that they would replace. Exotic optical components, precise alignment among the components, exact positioning of the different subsystems relative to each other, large size of the optical units--these attributes of prior optical interfaces all contribute to the failure to employ optical technology in electronics systems where multiple subsystems must communicate among each other over a common bus.